214 ELEMENTARY SCIENCE 



suppressed, not only because it is a nuisance, but also 

 because such suppression means greater economy in fuel 

 consumption. 



By holding a cold piece of iron in the flame, and re- 

 moving it before it gets too hot, you can collect drops of 

 water. This indicates that the candle contains hydrogen 

 as well as oxygen, and that this hydrogen is being oxi- 

 dized, thus forming water. Of course the heat causes this 

 water to be given off as invisible water vapor. 



Old-fashioned candles were made of tallow, which was 

 derived from animal fat. The molecules of fat are com- 

 posed of just three elements: carbon, hydrogen, and 

 oxygen. Modern candles are usually made from substances 

 derived from petroleum, but, like tallow, these substances 

 are composed of carbon, hydrogen, and oxygen only. So 

 evidently when we have collected carbon, carbon dioxide, 

 and water from the burning of a candle, we have accounted 

 for all the substances which compose it. 



The flame of a candle is cone-shaped. The center of 

 this cone, as you have proved by collecting carbon from it, 

 is composed of substance transformed by heat into a gaseous 

 state, but not yet completely oxidized. It is oxidized 

 when it reaches the surface of the cone, the part which is 

 luminous. You can prove the presence of unconsumed 

 gases in the center of a candle flame by introducing there 

 the end of a small glass tube. If you hold a match at 

 the other end of this tube, a flame will appear. 



Energy Released by Combustion. Thus far we have 

 discussed only the substances resulting from combustion. 

 But we are also familiar with the fact that, in combustion, 

 energy is released. This energy, in cases of burning, we 



